Amid the advance of miniaturization and multi-functionalization of various electronics, semiconductor chips to be mounted thereon are similarly required to achieve miniaturization and thinning. For the purpose of achieving thinning of the chip, it is general to grind the back face of a semiconductor wafer to perform thickness adjustment. In addition, a method which is called as the dicing before grinding method in which after forming a groove having a predetermined depth from the front face side of a wafer, grinding is performed from the wafer back face side, thereby achieving singulation of the chip by the grinding is occasionally utilized. In the dicing before grinding method, the back face grinding of the chip and the singulation of the chip can be simultaneously performed, and therefore, it is possible to efficiently produce a thin type chip. Further, in the dicing before grinding method, in addition to the method in which after forming a groove having a predetermined depth from the front face side of a wafer, grinding is performed from the wafer back face side as described above, there is also a method in which a modified layer is provided in the inside of the wafer by using a laser, and singulation of the chip is performed by a pressure, etc. at the time of wafer back face grinding.
Conventionally, at the time of back face grinding of a semiconductor wafer, in order to protect the circuit of the wafer front face and to fix the semiconductor wafer and the singulated semiconductor chips, it is general to stick a pressure sensitive adhesive tape called as a back grind sheet to the wafer front face. As the back grind sheet which is used in the dicing before grinding method, there is known a pressure sensitive adhesive sheet including a base and a pressure sensitive adhesive layer provided on one face of the base, wherein a buffer layer is further provided on the other face side of the base.
In the back grind sheet, by providing the buffer layer, it is possible to relieve a vibration generated at the time of wafer back face grinding. In addition, in the semiconductor wafer, in view of the matter that at the time of back face grinding, the wafer front face side on which the back grind sheet is provided is adsorbed on a chuck table, the semiconductor wafer is fixed to the table; however, it is also possible to absorb irregularities to be caused due to a foreign substance, etc. existent on the table by the buffer layer. The back grind sheet prevents cracking of the semiconductor wafer, chipping of the chip, etc. as generated at the time of back face grinding due to the forgoing actions of the buffer layer.
In addition, PTL 1 discloses a pressure sensitive adhesive sheet including a base, a pressure sensitive adhesive layer, and a buffer layer as described above, wherein the base is regulated to have a thickness of 10 to 150 μm and a Young's modulus of 1,000 to 30,000 MPa; and the buffer layer is regulated to have a thickness of 5 to 80 μm and a maximum value of tan δ of dynamic viscoelasticity of 0.5 or more. PTL 1 discloses that by using this pressure sensitive adhesive sheet as a back grind sheet in producing a semiconductor chip by the dicing before grinding method, chipping and discoloration of the chip can be prevented.